Another line later tapped into the Colorado River, but it also wasn’t enough to sustain the growth boom across Southern California. Yet another then dipped into the sensitive Sacramento-San Joaquin Bay Delta, but its southern stream now has been cut by a third.

The semiarid Southland imports more than half its water from hundreds of miles away through some of the modern world’s largest aqueducts. But water officials now say that in the decades ahead, it may not be enough — that more must be done to conserve and develop more water supplies here at home.

“We’ve been managing on the same amount of imported water since 1990 — we had 14 million (people) then, we’re now at 19 million,” said Jeff Kightlinger, general manager of the Metropolitan Water District, which serves 26 cities and water agencies from San Diego to Ventura to San Bernardino counties.

“And that’s our future: Using the same amount of water for more people. The price of water will likely grow a little faster than inflation.”

While Los Angeles commemorates its L.A. Aqueduct centennial Tuesday with a noon re-enactment of how chief water engineer William Mulholland ushered a northern mountain river down a San Fernando Valley cascade on Nov. 5, 1913, water visionaries across the region look toward the future to develop enough water to supply the vast dry region for the decades to come.

Since that day, Southern California grew to become a garden paradise of manicured lawns, kidney-shaped pools, golf links and gushing fountains, and pushed the boundaries of a nearly desert civilization.

The West has been dry for millions of years, with hugely varying annual rainfall, climatologists say. The Southland gets an average of 15 inches a year — enough water to supply 5 million people. But that can range from the 3 inches that Los Angeles eked by with seven years ago, to the 38 inches dumped on it during an El Niño season.

Longer cycles could bring severe drought. The 11th century saw an 80-year drought, long enough to wipe out a tribe of pre-Columbian Pueblo peoples. With the exception of a few water heavy storms, it’s been drier than normal for a decade.

With the influx a century ago of Eastern and Midwestern settlers to Los Angeles and Southern California, young cities began to look far afield for a reliable source of water — namely the snowmelt from the High Sierra and eastern Rockies.

What they didn’t realize, according to Southern California climate guru Bill Patzert, was the 20th century they were entering was among the wettest centuries in 2,000 years. And that climate change would shorten the mountain snow season, which acts as a frozen reservoir for the region’s water.

“We built a civilization in Southern California based on great water projects — we have the best water infrastructure in any place in the world,” said Patzert, climatologist for the Jet Propulsion Laboratory in La Cañada-Flintridge. “The problem is, now that we’re 70 percent dependent on imported water, the snow in the Sierras has been dry for a decade; the Colorado River has been dry for eight years.

“Now everybody wants water in the American Southwest and the water supply in the past decade has decreased.”

Beginning with the Los Angeles Aqueduct and a later pipeline to divert the distant Owens River, engineers looked to construct an aqueduct empire.

The Colorado River Aqueduct opened in 1939 to create the mighty Hoover and Parker dams and generate enough hydroelectric power to pump water from a river now shared by seven states and six Indian nations.

Supplies have been hampered in recent years by continued drought and quagga mussels, whose rapid proliferation can clog waterways and filtration systems. Both Lake Powell and Lake Mead — major reservoirs on the Colorado River — are less than half full.

The State Water Project opened in 1964 and now supplies water for 25 million Californians and agriculture for millions more. But now its levees are vulnerable to rising sea levels, extreme flood and a major earthquake. And dozens of species of fish and wildlife have been adversely threatened.

To protect the environment, a federal court six years ago ordered its water shipments cut by up to a third. To fix it, the state has proposed a controversial $25 billion Bay Delta Conservation Plan. Draft environmental documents are expected to be available for public comment in November.

The State Water Project provides a third of the Southland’s water.

In the meantime, Southern California water officials have devised long-term plans to reduce imported water and establish reliable supplies at home.

Last month, the MWD announced 16 projects designed to increase the use of recycled water, stormwater capture, desalted ocean water and recover enough groundwater to meet Southern California water needs.

The agency also launched new initiatives for enhancing water use efficiency, including rebates for rain barrels and soil moisture sensor systems, and incentives for retrofitting fitness centers with high-efficiency urinals and toilets.

The focus has been to comply with a state law that demands each city lower residential water use by 20 percent per person by 2020. By 2035, it aims for two-thirds of water demands be met by local resources, or a combined use of local water supplies like groundwater and conservation and recycling.

This month, the MWD announced it had enough reserves to meet water demands next year despite dry conditions, low water supplies and reduced deliveries of imported water. But worries remain.

“If this winter does not deliver abundant rain and snow, shortages in some regions of the state are likely next year,” said Mark Cowin, director of the state Department of Water Resources, in a statement. “We need Southern Californians to keep up their water conservation that sets a good example for all of the state.”

Los Angeles, the nation’s leading large city in water conservation, is already ahead of the game, according to the Department of Water and Power. Among other steps, last summer the agency launched a $300,000 study on additional ways to save water.

On an average year, the city’s 4 million residents now get more than a third of their water from the L.A. Aqueduct, half their water from imports by the Metropolitan Water District, 11 percent from groundwater and 1 percent from reclaimed sewer water.

By 2025 — 10 years ahead of its long-term projections — the city expects to cut its Delta and Colorado imports in half, while boosting groundwater use to 16 percent, recycled sewer water to 8 percent, water conservation to 9 percent and stormwater capture to 3 percent.

The city now has plans to clean up half the San Fernando Valley groundwater wells now contaminated by postwar industrial pollution.

It aims to replenish those wells with recycled sewer water, with extra layers of high-tech cleansing based on a successful “potable reuse” project employed since 2007 by Orange County.

It aims to help residents conserve water with incentives to swap lawns for low-water vegetation — paying them $2 a foot to do it — while employing smart water meters and drip irrigation systems.

And the city aims to recapture stormwater in large parking lots like the L.A. Zoo, or spreading grounds such as Big Tujunga Dam.

“I kind of liken it as a more sustainable version than what the city did with its L.A. Aqueduct,” DWP General Manager Ron Nichols said. “We are looking to now invest more in local water supply options.

“I think if we undertake these efforts, we’ll have a reliable and affordable supply of water for decades to come.”

Others say there may be a much easier water fix for cities cross the state.

California ranked No. 1 in the nation two years ago in agriculture, with 81,500 farms generating $43.5 billion in farm sales, or 12 percent of the U.S. total, according to the U.S. Department of Agriculture.

Yet agriculture contributed less than 3 percent of the state’s overall economy, Patzert said, while using three quarters of the state’s water on heavy water-use crops like rice and cotton. He blamed politics, bad water management and unfair water distribution.

“The bottom line is, we have a helluva lot of water,” Patzert said. “But we can’t do business as usual. How can agriculture use 70 percent of our water? And how can the fine folks of Beverly Hills be living in a rain forest? It’s a question of rethinking your priorities.

“If you want the California economy to continue to grow, we’ve got to make a few adjustments. The limiting factor is water — that is true of all civilizations.”

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